The Saracens had several times attacked it in the seventh century a.d., only to withdraw bloody and defeated from its walls. The Bulgars had twice laid siege to it, and did not relinquish their ambition until the great Emperor Basil II, the Bulgar-Slayer, put an end to the Bulgarian menace by sending 15,000 of their defeated army blinded, back to their homes. The Russians under Prince Igor had come down in a great fleet from the Black Sea in 1043 and had unwisely assailed the seaward walls. But then, as the chronicler described it, “liquid fire shot out upon our ships from long tubes placed in the parapets”, so that the panic-stricken attackers later described how “The Greeks have a fire like the lightning of the skies. They cast it against us and burned us so that we could not conquer them…”

But the city was defended in the eyes of its inhabitants, not only by mechanical inventions and by its soldiers. Not for nothing was it known as the ‘God-guarded City’, for within its walls lay the True Cross on which Christ had been crucified, the drops of blood he had shed at Gethsemane and innumerable other relics of great power. They ranged from the stone on which Jacob had laid his head to sleep, the rod of Moses and the head of John the Baptist, to fragments and relics of almost every apostle and saint in the history of the Church.

As soon as the fleet had assembled in the anchorage off St. Stephen’s Abbey, the Doge and the leaders of the Crusaders landed and held a conference. The Doge knew Constantinople better than any other member of the council. He had conducted a Venetian mission to the city over thirty years before, to sue for peace after the disasters that had befallen Venice in the war between the Republic and the Byzantine Empire. Dandolo had every reason to remember Constantinople, for it was during his stay within its walls that he had lost his eyesight. Whether this was due to a wound in the head (as Villehardouin asserts), to an illness, or—as was later maintained—to his being deliberately blinded by a burning-glass, the fact remains that the Doge had nourished an implacable hatred against the Byzantines ever since. His mission had proved unsuccessful, but his hatred of Constantinople was far deeper than any rancour that could possibly be due to a diplomatic failure. Under whatever circumstances the Doge had lost his eyesight, there seems little doubt that he held the city to blame. While the barons around him might be discussing the beauties of its towers and the formidable grandeur of its walls, Enrico Dandolo could only remember them—the colours of Santa Sophia, the green trees in the Emperor’s gardens, the shipping on the Golden Horn and the multihued aspect of Byzantium.

His advice to the assembly was succinct. They should not attempt the city from overland, for the soldiers would scatter in search of food (of which they were already short), and the army would quickly disintegrate into a rabble. He told them that the solution lay across the Marmora, where the Princes’ Islands shimmered under the sun, some ten miles away to the east, “There!” he said. “Those islands are inhabited by farmers. We can get corn and meat from them. Let us sail over and collect whatever provisions we need, and then proceed to take up our positions off the city. The fighting man who has a bellyfull of food acquits himself better than the man who is hungry.”

But the following morning when the fleet weighed anchor, the wind had gone round to the south and was blowing straight up the Marmora. There could be no question of making for the Princes’ Islands, so the ships took the wind under their sterns and made their way up the narrow strait towards the city. Now, for the first time, they could really see and appreciate the grandeur and immensity of its seaward walls. Although they were single walls and far simpler than the elaboration of ditches, double-walls and fortifications on the landward side, they rose sheer from the water. These seaward defences on the Marmora had been restored and strengthened by the Emperor Theodosius in the fifth century. Although the subsequent misspending of Byzantine revenues by weak and indifferent emperors had failed to maintain them at their best, yet they still appeared unassailable. Furthermore, they had two important natural protections: the fast current which swept down the Bosphorus and which would render it almost impossible to beach a landing-craft and hold it in position while the troops got ashore; and the innumerable rocks and shoals which fringed the coastline and presented a dangerous hazard to any without expert local knowledge.

The day on which the Venetians and Crusaders sailed past the walls of Constantinople was dedicated in the Church Calendar to St. John the Baptist (whose head in its enamelled gold and gem-studded reliquary was one of the city’s divine sources of protection). To honour the saint, the ships were dressed overall with banners and pennons, while every man entitled to a coat-of-arms had his shield displayed over the bulwarks. The Comte de Villehardouin was certainly under no illusion that the restoration of young Alexius was likely to be acceptable to the Byzantines, for he noted that “every man was assiduous in cleaning and preparing his arms and armour, for no one was in any doubt but that they would soon have need of them”.

In order to assess the quality and nature of the defences, the fleet passed as close to the walls of the city as was consistent with safe navigation.